1. Field of the Invention
The present invention relates to a hemispheric fluid bearing apparatus, and more particularly to a hemispheric fluid bearing apparatus, without a spacer, capable of adjusting a clearance between hemispheres and a bushing.
2. Description of the Prior Art
Recently, with improvements in the fields of information and computer technologies, computers, audio systems and image devices have become more compact, as a result there has arisen a need for parts of the computer, the audio system, and the image device to have high accuracy.
Driving motors for various machines such as a spindle motor of a hard disk drive in the field of auxiliary memory devices, a scanning motor of a laser printer in the field of computers, a driving apparatus for driving a laser disk and a compact disk in audio systems, and a head driving motor of a video cassette recorder and a camcorder, commonly rotate a rotary shaft mounted in the driving motors with high velocity to carry out recording and reproducing of data.
The rotary shaft rotates at very high velocity while creating an oscillation and a vibration. Thus, the computer, the laser printer, the audio system, the video cassette recorder, the camcorder, and the like which use the rotary shaft, may experience critical defects.
Accordingly, bearings are used for overcoming the problems generated by the high velocity rotation of the rotary shaft of the driving motor. There are several kinds of bearings, but, preferably, a fluid bearing apparatus is used for the rotary shaft rotating at high velocity.
A driving device for driving a polygon mirror of a laser printer, to which a hemispheric fluid bearing is applied, will be described in detail with reference to FIG. 1.
The driving device for driving a polygon mirror 10 includes a fixed shaft 20 which acts as a rotating center of the polygon mirror 10, hemispheres 30 and 35 which are press-fitted to the fixed shaft 20 and have spheric surfaces with high spherity, a bushing 40 for supporting a radial load and a thrust load of the hemispheres 30 and 35, a rotor 55 and a stator 50 which are a driving device, a hub 60, and a housing 70.
In an assembling of the polygon mirror 10, the fixed shaft 20, the hemispheres 30 and 35, and the bushing 40, the fixed shaft 20 is press-fitted to the housing 70 to which the hemispheres 30 and 35 are press-fitted. Dynamic pressure generating grooves (not shown) are formed on spheric surfaces of the hemispheres 30 and 35 in order to generate a predetermined fluid pressure. Furthermore, the hub 60 is assembled to the bushing 40, on which the rotor 55 and the polygon mirror 10 are mounted. In the result, hemispheres 30 and 35 are fixed to the shaft 20 which is press-fitted to the housing 70 while the bushing 40 rotates around the shaft 20.
The bushing 40 for supporting the radial load and the thrust load has a through hole having a diameter larger than that of the shaft 20 perforated, in which hemispheric grooves 30a and 35a are formed at both ends thereof to be opposite to each other. A curvature of the hemispheric grooves 30a and 35a is same as that of the hemispheres 30 and 35 which are press-fitted to the fixed shaft 20. Also, a spacer 40a is inserted into the throughhole of the bushing 40 so as to adjust a clearance between the hemispheres 30 and 35 and the bushing 40.
An operation of the hemispheric fluid bearing apparatus according to the conventional art, as constructed above, will be described in detail.
When electric power is applied to the stator 50 and the rotor 55 so that the bushing 40 rotates, the bushing 40 moves downwardly by means of self-weight so as to be in close contact with the lower hemisphere 30. Thus, the upper hemisphere 35 is spaced from the bushing 40 by several .mu.m. As a result, the dynamic pressure is higher at the lower hemisphere 30 having the smaller clearance between the bushing 40 than at the upper hemisphere 35 having the larger clearance between the bushing 40. This uneven distribution of the bushing causes vibrations and other problems.